Rendering of objects visible in viewport only!
By default only the eye icon to hide the object in the viewport is shown in the outliner, but you can add other icons including one to prevent the object being rendered.  Click on the Filter icon above the outliner then on the camera icon in the menu that appears. Hover over each icon for a description of what it does.

You'll then find another column of camera icons in the outliner which you can use to prevent the object being rendered as shown below.